1. Field of the Invention
The present invention relates to a photographic printing method and system, and more particularly, to a printing method and system in which a neutral density (ND) filter is used for printing an image having a low large area transmittance density (LATD).
2. Description of the Related Art
In order to perform photofinishing efficiently at a large laboratory, 50 to 100 rolls of photographic film are spliced together to obtain a spliced long film. This long film is loaded into a film processor, developed, and supplied to a notch puncher which performs a film inspection. At the notch puncher, a frame is automatically detected, and original frames are sequentially supplied to an inspection station. An original frame supplied to the inspection station is visually checked to determine whether it is to be printed. If it is to be printed, a semicircular notch is formed in the side portion on a central line of the original frame.
Next, the long film is loaded into a film analyzer (also called a scanner), and original frames are sequentially supplied to a photometry station. An image sensor is provided at the photometry station to measure a transmittance density of each point of the original frame. A minimum density, a maximum density, an LATD at the central area of the frame, an LATD at the peripheral area of the frame, an LATD at the upper half area of the frame, and an LATD at the lower half of the frame are obtained from the transmittance density at each point of the original frame. In accordance with these characteristic values, scenes of original frames are classified. In accordance with the scene classification, an exposure correction amount is calculated. This exposure correction amount is written into a storage medium such as a paper tape, a magnetic tape, or an LSI card.
The long film and storage medium are removed from the film analyzer and are loaded into an auto-printer. Each original frame of the long film is automatically and sequentially supplied to a print station within the auto-printer, and an average transmittance density of the whole area of the frame (LATD) is measured. An exposure time is calculated from the LATD and the exposure correction amount read from the storage medium. The original frame is printed at this exposure time onto a photographic paper. After all of the original frames of the long film have been printed, the photograph paper is developed by a paper processor, and thereafter it is cut into each photoprint.
In the case of a color negative film, a color image sensor is used to measure three primary colors including red, green, and blue at each point of an original frame. By using an average value (grey density) of the three colors, a scene classification is carried out. In accordance with the scene classification, exposure correction amounts for the three colors are calculated. At the auto-printer, three sensors measure LATDs of red, green, and blue. In accordance with the LATDs and exposure correction amounts for the three colors, an exposure time for each color is calculated. The control of the exposure time for each color is performed by a black shutter, a red cut-filter (cyan filter), a green cut-filter (magenta filter), and a blue cut-filter (yellow filter). Specifically, after the black shutter is opened and an exposure time of some color lapses, the corresponding cut-filter is inserted into a printing path.
Since the exposure time is related to an LATD of an original frame, the exposure time becomes very short, such as several tens of milliseconds (ms), in the case of an under exposed frame having a low LATD exposure. If the exposure time is short, the influence of an operation delay time of the black shutter or cut-filter becomes significant, resulting in incorrect exposure control. In order to set an exposure time for an under exposed frame to a proper time, a printing light source having a small light emission intensity is used. However, with the printing light source having a small light emission intensity, an exposure time of a properly exposed frame or of an over exposed frame is increased, thereby preventing high speed printing.
In order to deal with the above problems, a method has been proposed as disclosed in Japanese Patent Publication No. 59-7374, wherein a light source having a large light emission intensity is used, and an ND filter is used for an under exposed frame to elongate an exposure time. With this printing method, an original frame to be printed is first supplied to a print station to calculate an LATD of each color of the original frame. Next, if the minimum value of LATDs for the three colors is lower than the transmittance density of a normal control frame, the density value of an ND filter corresponding to the difference between the minimum value and the transmittance density of the normal control frame is obtained. An ND filter having such a density value is inserted into the printing path to print an under exposed frame.
The density of an ND filter is lowered by a time dependent change such as fading and stains. According to the conventional method, the ND filter density is used before a time dependent change has occurred so that proper exposure control is difficult. Furthermore, the ND filter density is determined after the photometry of an original frame at the print station. Therefore, printing can be started only after an ND filter is inserted into the printing path which prevents high speed printing.